Re-up is a slang often used by drug dealers to describe the act of replenishing their drug supply when it gets low. Re-up is short for "Reload Up." Whatever product is purchased when a dealer re-ups, is also referred to as "Re-Up." This slang is heavily used in Hip Hop music, in Biggie's "Tonight" song, he raps, "Guard your sh*t, 'fore I stick you for your re-up."